近日，美国研究者发现，在动物饲料中添加抗生素会产生令人忧虑的效果：药物会刺激动物肠道内的病毒在肠道细菌间转移基因。如此一来，令肠道细菌对抗生素产生耐药性的基因就会被大量转移。科学家在专业期刊《微生物学》(Microbiology)上撰文警告称，激活这些病毒会导致耐药性在细菌间大幅扩散。
人们早就知道，如果给猪或家禽喂食抗生素，那么这些动物的肠道细菌会大量产生耐药性。而现在研究者发现，特定病毒在耐药性的扩散过程中发挥着重要作用。大部分遗传信息并不是在细菌间直接传递的，而是借助于噬菌体。
噬菌体在休眠阶段只是细菌遗传物质中的一小段脱氧核糖核酸。然而，一旦受到刺激，它们就会突变成真正的病毒：这些病毒会在细菌细胞内爆炸性地复制，然后大量冲出细胞，最终冲入其他细菌细胞内，将遗传信息注入这些细菌的遗传物质。
研究者称，他们现在首次研究了抗生素对这种噬菌体的影响。研究表明，药物促进了病毒的激活过程。研究者发现，与未服用抗生素的猪相比，服用了抗生素的猪的肠道内被释放出的噬菌体要多得多。
“这一发现很有意义，因为人们知道噬菌体会转移耐药性基因”，希瑟·艾伦说。她是论文的第一作者，任职于美国农业部动物疾病中心。一旦噬菌体的活动致使耐药性基因在细菌间广泛传播，那么这些基因被转移给人类病原体的危险也就增加了——例如在家禽和家畜的肠道内。（生物谷Bioon.com）
doi:10.1128/mBio.00260-11
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Antibiotics in Feed Induce Prophages in Swine Fecal Microbiomes
Heather K. Allena, Torey Loofta, Darrell O. Baylesb, Samuel Humphreya, Uri Y. Levinea, David Altb, and Thaddeus B. Stantona
Antibiotics are a cost-effective tool for improving feed efficiency and preventing disease in agricultural animals, but the full scope of their collateral effects is not understood. Antibiotics have been shown to mediate gene transfer by inducing prophages in certain bacterial strains; therefore, one collateral effect could be prophage induction in the gut microbiome at large. Here we used metagenomics to evaluate the effect of two antibiotics in feed (carbadox and ASP250 [chlortetracycline, sulfamethazine, and penicillin]) on swine intestinal phage metagenomes (viromes). We also monitored the bacterial communities using 16S rRNA gene sequencing. ASP250, but not carbadox, caused significant population shifts in both the phage and bacterial communities. Antibiotic resistance genes, such as multidrug resistance efflux pumps, were identified in the viromes, but in-feed antibiotics caused no significant changes in their abundance. The abundance of phage integrase-encoding genes was significantly increased in the viromes of medicated swine over that in the viromes of nonmedicated swine, demonstrating the induction of prophages with antibiotic treatment. Phage-bacterium population dynamics were also examined. We observed a decrease in the relative abundance of Streptococcus bacteria (prey) when Streptococcus phages (predators) were abundant, supporting the “kill-the-winner” ecological model of population dynamics in the swine fecal microbiome. The data show that gut ecosystem dynamics are influenced by phages and that prophage induction is a collateral effect of in-feed antibiotics.
